[R-390] Mechanical filter Alignment

[Gordon]

Thanks Roger,
   I appreciate the tips. I am trying to track down why it distorts on 
very strong signals. It's as if the AGC isn't fast enough on the Attack 
time.
Perhaps my C551 is Bad. I seem to have read some where that the AGC 
is/can be a problem on the 390A receivers.

73,
Gordon
N6WK

On 5/26/2013 2:57 PM, Roger Ruszkowski wrote:
>
>
> Gordon,
>   
> In the beginning there was no adjustment.
> Some nice values were engineered and the
> best cap values were installed.
>
> The first production runs from Collins did not
> have trim caps. A fixed value was used.
>
> If you have one of these early decks be happy.
> You have one of the  original early IF deck modules.
>
> Look on the IF deck side of your receiver frame.
> Do you have a set of 4 holes in the side that lets you
> look at the IF deck where the trim caps under the
> IF deck could be adjusted?
>
> You hope not. So you also know if you
> have an old early frame (not holes) or
> a later production frame with holes.
>
> A lot of adjustable IF decks went into frames
> with no side holes. You tilted the deck out to do
> the trim cap adjustment. Then late model frames
> had holes added. Look out for hand drilled frames.
> Not a problem but you know its a post production change.
>   
> Some one though service people did not have enough
> to do and decided that caps to diddle were needed.
> So trim caps were added.
>   
> If your IF deck does not have them, then be blessed
> and leave it alone. It is good as it gets.
>   
> You just can not add them in.
> They are not needed.
>   
> Besides the caps do not align the filters at all.
> They just get a bit better or not better impedance
> match in and out of the filter for more of less
> signal level passed through the filter.
>   
> The Idea was not to align the filter.
> The idea was to adjust the four filters for the
> same relative power level. And this was not
> necessarily the maximum power through any of
> the filters.
>   
> Roger AI4NI
>   
>   
>
>
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